Endless belt, belt unit, and image forming apparatus

Abstract

To provide an endless belt that, when applied to transfer means that transfers a toner image to a recording medium, achieves both prevention of density unevenness of an image and prevention of generation of cracks in a base material layer.SOLUTION: An endless belt has a base material layer including polymeric material and conductive particles. In an image obtained by observing a cross section of the base material layer cut along a thickness direction by an atomic force microscope, the ratio of the total area Ap of the cross sections of the entire conductive particles is 9.0% or more and 14.5% or less with respect to the area At of the entire cross section of the base material layer, and in the cross section of the conductive particle, the ratio of the total area Ab of the cross sections of the conductive particles having an area of 0.01 μm2 or more is 28.0% or more and 65.0% or less with respect to the total area Ap of the cross sections of the entire conductive particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure provides an endless belt, a belt unit, and an image forming apparatus. [Background technology]

[0002] Patent Document 1 discloses an electrophotographic belt containing polyetheretherketone and carbon black dispersed in polyetheretherketone. Patent Document 2 discloses a semiconductive belt made of a polyimide resin containing carbon black, characterized in that the carbon black has a maximum particle size of 1.0 to 1.5 μm in secondary aggregation and a standard deviation of particle size distribution of 0.5 μm or less. Patent Document 3 discloses a semiconductive seamless belt made of a resin material and a carbon filler, characterized in that the average effective particle diameter of the carbon filler is 0.5 μm or less, the maximum effective particle diameter is 3 μm or less, and particles with an effective particle diameter of 1 μm or more constitute 2% by weight or less of the total amount of carbon filler. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-177811 [Patent Document 2] Japanese Patent Publication No. 2003-131463 [Patent Document 3] Japanese Patent Publication No. 2001-265130 [Overview of the project] [Problems that the invention aims to solve]

[0004] In an endless belt used as a transfer member in a transfer means that transfers a toner image to a recording medium by applying voltage, electric field dependence is required to improve transferability and suppress density unevenness in the image. This involves increasing resistance in low electric fields and decreasing resistance in high electric fields to allow a large amount of current to flow. One method for obtaining this electric field dependence is to incorporate conductive particles with a wide particle size distribution into the substrate layer of the endless belt in an appropriate amount. On the other hand, in an endless belt in which the substrate layer contains conductive particles with a wide particle size distribution, cracks may occur due to the non-uniformity of particle size in the conductive particles.

[0005] The embodiments of this disclosure aim to provide an endless belt having a substrate layer containing a polymer material and conductive particles, in which the ratio of area Ap to area At is less than 9.0% or greater than 14.5%, the ratio of area Ab to area Ap is less than 28.0% or greater than 65.0%, or the ratio of number Nb to number Np is less than 3.5% or greater than 13.7%, and in which case the endless belt, when applied to a transfer means for transferring a toner image to a recording medium, achieves both suppression of uneven image density and suppression of crack occurrence in the substrate layer. [Means for solving the problem]

[0006] The following embodiments are included as specific means for solving the aforementioned problems. <1> The substrate layer comprises a polymer material and conductive particles, In an image obtained by observing a cross-section cut along the thickness direction of the substrate layer using an atomic force microscope, the ratio of the total area Ap of the cross-sections of all the conductive particles is 9.0% or more and 14.5% or less of the total area At of the cross-sections of the substrate layer, and the area of ​​the cross-section of the conductive particles is 0.01 μm². 2 The ratio of the total cross-sectional area Ab of the conductive particles to the total cross-sectional area Ap of all conductive particles is 28.0% or more and 65.0% or less. Endless belt. <2> The ratio of the total cross-sectional area Ap of the conductive particles is 9.5% to 14.0% of the total cross-sectional area At of the substrate layer. <1> The endless belt described above. <3> The area is 0.01 μm 2 The ratio of the total cross-sectional area Ab of the conductive particles is 35.2% to 61.3% of the total cross-sectional area Ap of all conductive particles. <1> or <2> The endless belt described above. <4> The area of ​​the cross-section of the conductive particle is 0.005 μm 2 The above is 0.01 μm. 2 The proportion of the total cross-sectional area Am of conductive particles that is less than 16.1% to 21.8% of the total cross-sectional area Ap of all conductive particles. <1> ~ <3> An endless belt as described in any one of the following.

[0007] <5> The substrate layer comprises a polymer material and conductive particles, In an image obtained by observing a cross-section cut along the thickness direction of the substrate layer using an atomic force microscope, the ratio of the total area Ap of the cross-sections of all the conductive particles is 9.0% or more and 14.5% or less of the total area At of the cross-sections of the substrate layer, and the area of ​​the cross-section of the conductive particles is 0.01 μm². 2 The proportion of the number of conductive particles Nb in the cross-section is 3.5% or more and 13.7% or less of the total number of conductive particles Np in the cross-section. Endless belt. <6> The area of ​​the cross-section of the conductive particle is 0.005 μm 2 The above is 0.01 μm. 2 The proportion of the number of conductive particles in the cross-section Nm that is less than 7.5% to 13.5% of the total number of conductive particles in the cross-section Np is 7.5% or more. <5> The endless belt described above.

[0008] <7> The aforementioned polymer material includes ion-conductive rubber, <1> ~ <6> An endless belt as described in any one of the following. <8> The endless belt according to <7>, wherein the ion conductive rubber contains at least one selected from the group consisting of epichlorohydrin rubber and chloroprene rubber. <9> The endless belt according to any one of <1> to <8>, wherein the conductive particles contain electron conductive particles. <10> The endless belt according to <9>, wherein the electron conductive particles contain carbon black.

[0009] <11> The endless belt according to any one of <1> to <10>, wherein the average equivalent circle diameter in the cross section of the conductive particles is 26.7 nm or more and 43.8 nm or less. <12> The endless belt according to any one of <1> to <11>, further comprising a release layer provided on at least one of the outer peripheral surface and the inner peripheral surface of the base material layer. <13> The endless belt according to any one of <1> to <12>, and a plurality of roll members for passing the endless belt in a tensioned state, and is provided with detachable from the image forming apparatus, a belt unit. <14> a photoreceptor, and charging means for charging the surface of the photoreceptor, electrostatic charge image forming means for forming an electrostatic charge image on the surface of the charged photoreceptor, developing means for accommodating a developer containing toner and developing the electrostatic charge image formed on the surface of the photoreceptor with the developer to form a toner image, a transfer means having the belt unit according to <13> and transferring the toner image to a recording medium, An image forming apparatus comprising. <15> The transfer means has an intermediate transfer body, primary transfer means for transferring the toner image to the surface of the intermediate transfer body, and secondary transfer means for transferring the toner image transferred to the surface of the intermediate transfer body to a recording medium. The secondary transfer means comprises the belt unit described in claim 13, <14> The image forming apparatus described above. [Effects of the Invention]

[0010] <1> , <7> , <8> , <9> , <10> , or <12> According to the invention, an endless belt having a substrate layer containing polymer material and conductive particles is provided that, compared to cases where the ratio of area Ap to area At is less than 9.0% or greater than 14.5%, or the ratio of area Ab to area Ap is less than 28.0% or greater than 65.0%, when applied to a transfer means for transferring a toner image to a recording medium, achieves both suppression of uneven image density and suppression of crack occurrence in the substrate layer. <2> According to the invention, an endless belt is provided that suppresses density unevenness of the image when applied to a transfer means for transferring a toner image to a recording medium, compared to cases where the ratio of area Ap to area At is less than 9.5% or more than 14.0%. <3> According to the report, an endless belt is provided that, compared to cases where the ratio of area Ab to area Ap is less than 35.2% or more than 61.3%, achieves both suppression of uneven image density and suppression of crack occurrence in the substrate layer when applied to a transfer means for transferring a toner image to a recording medium. <4> According to the invention, an endless belt is provided that suppresses density unevenness of the image when applied to a transfer means for transferring a toner image to a recording medium, compared to cases where the ratio of area Am to area Ap is less than 16.1% or more than 21.8%.

[0011] <5> According to the invention, an endless belt having a substrate layer containing polymer material and conductive particles is provided that, compared to cases where the ratio of area Ap to area At is less than 9.0% or greater than 14.5%, or the ratio of number Nb to number Np is less than 3.5% or greater than 13.7%, can be applied to a transfer means for transferring a toner image to a recording medium, while simultaneously suppressing both the reduction of density unevenness in the image and the reduction of crack occurrence in the substrate layer. <6> According to the report, an endless belt is provided that suppresses density unevenness of the image when applied to a transfer means for transferring a toner image to a recording medium, compared to cases where the ratio of the number of particles Nm to the number of particles Np is less than 7.5% or more than 13.5%.

[0012] <11> According to the report, an endless belt is provided that, compared to cases where the average equivalent circle diameter in the cross-section of conductive particles is less than 26.7 nm or greater than 43.8 nm, achieves both suppression of uneven image density and suppression of crack occurrence in the substrate layer when applied to a transfer means for transferring toner images to a recording medium. <13> According to the invention, compared to a belt unit having an endless belt having a base layer containing a polymer material and conductive particles, where the ratio of area Ap to area At is less than 9.0% or greater than 14.5%, the ratio of area Ab to area Ap is less than 28.0% or greater than 65.0%, or the ratio of number Nb to number Np is less than 3.5% or greater than 13.7%, a belt unit is provided that, when applied to a transfer means for transferring a toner image to a recording medium, achieves both suppression of uneven image density and suppression of crack formation in the base layer of the endless belt. <14> According to the invention, compared to an image forming apparatus whose transfer means includes a belt unit comprising an endless belt having a base layer containing a polymer material and conductive particles, wherein the ratio of area Ap to area At is less than 9.0% or greater than 14.5%, the ratio of area Ab to area Ap is less than 28.0% or greater than 65.0%, or the ratio of number Nb to number Np is less than 3.5% or greater than 13.7%, an image forming apparatus is provided that can suppress both density unevenness in the image and the occurrence of cracks in the base layer of the endless belt. <15> According to the invention, compared to an image forming apparatus in which a secondary transfer means has a belt unit comprising an endless belt having a base layer containing a polymer material and conductive particles, where the ratio of area Ap to area At is less than 9.0% or greater than 14.5%, the ratio of area Ab to area Ap is less than 28.0% or greater than 65.0%, or the ratio of number Nb to number Np is less than 3.5% or greater than 13.7%, an image forming apparatus is provided that can suppress both density unevenness in the image and the occurrence of cracks in the base layer of the endless belt. [Brief explanation of the drawing]

[0013] [Figure 1] A schematic perspective view showing an example of an endless belt according to this embodiment. [Figure 2] This is a schematic perspective view showing an example of a belt unit according to this embodiment. [Figure 3] This is a schematic diagram showing an example of an image forming apparatus according to this embodiment. [Modes for carrying out the invention]

[0014] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0015] In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0016] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0017] When describing embodiments in the present disclosure with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Also, the sizes of members in each drawing are conceptual, and the relative relationships of the sizes between members are not limited to this.

[0018] In the present disclosure, each component may include a plurality of corresponding substances. When referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0019] [Endless belt] [First Embodiment] The endless belt according to the first embodiment has a base material layer containing a polymer material and conductive particles. In an image obtained by observing a cross-section cut along the thickness direction of the base material layer with an atomic force microscope, the ratio of the total cross-sectional area Ap of all the conductive particles to the cross-sectional area At of the entire base material layer is 9.0% or more and 14.5% or less, and among the cross-sections of the conductive particles, the ratio of the total cross-sectional area Ab of the conductive particles with an area of 0.01 μm 2 or more is 28.0% or more and 65.0% or less with respect to the total cross-sectional area Ap of all the conductive particles.

[0020] Hereinafter, the ratio of the total area Ap to the cross-sectional area At is also referred to as "total particle area ratio (%)". Also, conductive particles with an area of 0.01 μm 2 or more are referred to as "large-diameter particles", and conductive particles with an area of 0.005 μm 2 or more and less than 0.01 μm 2 are referred to as "medium-diameter particles", and conductive particles with an area of less than 0.005 μm 2 are also referred to as "small-diameter particles". Also, the ratio of the total cross-sectional area Ab of the large-diameter particles to the total area Ap is referred to as "large-diameter area ratio (%)", and the ratio of the total cross-sectional area Am of the medium-diameter particles to the total area Ap is referred to as "medium-diameter area ratio (%)". Also, conductivity means that the volume resistivity at 20°C is less than 1×10 13 Ωcm.

[0021] Here, the endless belt according to the first embodiment is used, for example, incorporated as part of a transfer means in an electrophotographic image forming apparatus. The endless belt according to the first embodiment is used, for example, as a transfer member (e.g., a secondary transfer belt or an intermediate transfer belt) of a transfer means that transfers a toner image to a recording medium. The endless belt according to the first embodiment transports, for example, a recording medium or a toner image.

[0022] The endless belt used as a transfer member in a transfer means for transferring a toner image to a recording medium should preferably have a characteristic in which its electrical resistance clearly changes depending on the applied voltage. For example, it is desirable that there be a clear difference between the resistance value at an applied voltage of 100V and the resistance value at an applied voltage of 500V. This results in the endless belt having relatively high resistance when the transfer process is not in operation, making the surface of the endless belt less resistant to toner, while the endless belt has relatively low resistance when the transfer process is in operation, resulting in excellent transfer performance. Transfer performance can be evaluated, for example, by the density unevenness of the image.

[0023] Thus, when using an endless belt as a transfer member in a transfer means that transfers a toner image to a recording medium by applying voltage, in order to improve transferability and suppress density unevenness in the image, "electric field dependence" is required, which involves increasing resistance in low electric fields and decreasing resistance in high electric fields to allow a large amount of current to flow. If the endless belt has electric field dependence, it will decrease in resistance in high electric fields, so in a low temperature and low humidity environment of 10°C and 15% humidity (hereinafter also referred to as "Cz"), a small voltage and small current will be required, making it less likely for color loss (e.g., white spots) caused by abnormal discharge to occur. In addition, in low electric fields, the increased resistance promotes self-static discharge, making it less likely for the image history of the previous cycle to affect the next cycle, and thus reducing density unevenness.

[0024] One method for obtaining this electric field dependence is to incorporate conductive particles with a broad particle size distribution into the substrate layer of the endless belt in an appropriate amount. Conductive particles with a broad particle size distribution have relatively large diameter particles and relatively small diameter particles. However, in endless belts where the substrate layer contains conductive particles with a large particle size distribution, cracks (hereinafter also referred to as "cracks") may occur due to the non-uniformity of particle size in the conductive particles. Specifically, for example, if the base layer of an endless belt contains conductive particles having relatively large diameter particles and relatively small diameter particles, repeated deformation during use can cause stress to concentrate locally on the large diameter particles, potentially leading to cracks in the base layer.

[0025] In contrast, the endless belt according to the first embodiment has a total particle area ratio within the aforementioned range, and a large-diameter area ratio that is larger than that of conventional belts and within the aforementioned range. Therefore, when applied to a transfer means for transferring a toner image to a recording medium, it achieves both suppression of density unevenness in the image and suppression of crack occurrence in the substrate layer. The reason for this is not clear, but it is presumed to be as follows.

[0026] First, the above total particle area ratio corresponds to the content of conductive particles in the entire substrate layer. When the total particle area ratio is within the above range, the overall resistance of the endless belt is not too high compared to when it is lower than the above range, resulting in an endless belt suitable as a transfer material. Furthermore, when the total particle area ratio is within the above range, excessive current flow under low electric fields is suppressed compared to when it is higher than the above range, making it easier to obtain electric field dependence.

[0027] In the first embodiment, the total particle area ratio is kept within the aforementioned range, while the large-diameter area ratio is also kept within the aforementioned range. In this case, in an endless belt where the total particle area ratio is within the aforementioned range and the large-diameter area ratio is smaller than the aforementioned range, the number of large-diameter particles contained in the base layer is small. In other words, by keeping the large-diameter area ratio within the aforementioned range, stress is more easily distributed among a moderate number of large-diameter particles compared to the case where the large-diameter area ratio is smaller than the aforementioned range, and it is thought that crack generation due to stress concentration on the few scattered large-diameter particles is suppressed. Furthermore, in an endless belt having a base layer where the total particle area ratio is within the aforementioned range and the proportion of large-diameter particles is greater than the aforementioned range, the number of small-diameter and medium-diameter particles is small. In other words, because the proportion of large-diameter particles is within the aforementioned range, the number of small-diameter and medium-diameter particles is not too small compared to the case where the proportion of large-diameter particles is greater than the aforementioned range, making it easier to obtain electric field dependence and suppressing stress concentration on large-diameter particles.

[0028] For the reasons stated above, it is presumed that the endless belt according to the first embodiment can achieve both suppression of uneven image density and suppression of crack occurrence in the substrate layer when applied to a transfer means for transferring a toner image to a recording medium.

[0029] <Second Embodiment> The endless belt according to the second embodiment has a base layer containing a polymer material and conductive particles, and in an image obtained by observing a cross-section cut along the thickness direction of the base layer with an atomic force microscope, the ratio of the total area Ap of the cross-sections of all the conductive particles is 9.0% or more and 14.5% or less of the total area At of the cross-section of the base layer, and the area of ​​the cross-section of the conductive particles is 0.01 μm². 2 The proportion of the number of conductive particles Nb in the cross-section is 3.5% to 13.7% of the total number of conductive particles Np in the cross-section.

[0030] Hereinafter, the ratio of the number of large-diameter particles in the cross-section Nb to the total number of conductive particles in the cross-section Np will also be referred to as the "large-diameter particle ratio (%)", and the ratio of the number of medium-diameter particles in the cross-section Nm to the total number of conductive particles in the cross-section Np will also be referred to as the "medium-diameter particle ratio (%)".

[0031] Here, as described above, the endless belt according to the second embodiment is used, for example, incorporated as part of a transfer means in an electrophotographic image forming apparatus. The endless belt according to the second embodiment is used, for example, as a transfer member (for example, a secondary transfer belt or an intermediate transfer belt) of a transfer means that transfers a toner image to a recording medium. The endless belt according to the second embodiment transports, for example, a recording medium or a toner image.

[0032] As described above, an endless belt used as a transfer member in a transfer means that transfers a toner image to a recording medium by applying a voltage is required to have electric field dependence in order to suppress density unevenness of the image. Furthermore, as described above, if conductive particles with a wide particle size distribution are included in the substrate layer of the endless belt in an appropriate amount in order to obtain electric field dependence, cracks may occur in the substrate layer of the endless belt due to the non-uniformity of the particle size of the conductive particles.

[0033] In contrast, the endless belt according to the second embodiment has a total particle area ratio within the aforementioned range, and a large-diameter area ratio that is larger than that of the conventional belt and is within the aforementioned range. Therefore, when applied to a transfer means for transferring a toner image to a recording medium, it achieves both suppression of density unevenness in the image and suppression of crack occurrence in the substrate layer. The reason for this is not clear, but it is presumed to be as follows.

[0034] As described above, the total particle area ratio corresponds to the content of conductive particles in the entire substrate layer. When the total particle area ratio is within the above range, the overall resistance of the endless belt is not too high compared to when it is lower than the above range, resulting in an endless belt suitable as a transfer material. Compared to when it is higher than the above range, excessive current flow under low electric fields is suppressed, and electric field dependence is more easily obtained.

[0035] In the second embodiment, the total particle area ratio is kept within the aforementioned range, while the proportion of large-diameter particles is kept within the aforementioned range. This makes it easier for stress to be distributed among a sufficient number of large-diameter particles compared to the case where the total particle area ratio is within the aforementioned range and the proportion of large-diameter particles is smaller than the aforementioned range, thus suppressing crack generation due to stress concentration on the few scattered large-diameter particles. Furthermore, by keeping the total particle area ratio within the aforementioned range and the proportion of large-diameter particles within the aforementioned range, it is thought that the number of small-diameter and medium-diameter particles is not too small compared to the case where the total particle area ratio is within the aforementioned range and the proportion of large-diameter particles is larger than the aforementioned range, making it easier to obtain electric field dependence and suppressing stress concentration on large-diameter particles.

[0036] For the reasons stated above, it is presumed that the endless belt according to the second embodiment can achieve both suppression of uneven image density and suppression of crack occurrence in the substrate layer when applied to a transfer means for transferring a toner image to a recording medium.

[0037] Hereinafter, an endless belt that corresponds to either the endless belt according to the first embodiment or the endless belt according to the second embodiment will be referred to as the "endless belt according to this embodiment" and described accordingly. However, an example of the endless belt of the present invention is an endless belt that corresponds to at least one of the endless belt according to the first embodiment or the endless belt according to the second embodiment. The endless belt according to this embodiment will be described in detail below.

[0038] <Cross-sectional observation of the substrate layer> Cross-sectional observation of the substrate layer is performed as follows. -Sample preparation- Using the cryomicrotome method, the endless belt is cut parallel to the width direction and in the thickness direction to prepare section samples. Section samples are prepared at a total of 20 locations: 5 locations at equal intervals in the width direction of the endless belt (i.e., evenly distributed from near one end to near the other end) and 4 locations at equal intervals in the circumferential direction. The cross-sections of 20 individual samples were observed using an AFM (atomic force microscope) in a 5 μm x 5 μm square area to obtain phase images. For each of the 20 phase images, Otsu's binarization process was applied to a square area using image analysis software, and the dark areas were identified as conductive particles.

[0039] -Area ratio of conductive particles- All conductive particles (i.e., point-like dark areas) within the binarized rectangular region are to be measured. The area of ​​each conductive particle is measured, and the areas of all conductive particles are summed up to calculate the ratio of the area of ​​the conductive particles (i.e., the total area of ​​the cross-section of all conductive particles Ap) to the area of ​​the rectangle (i.e., the total area of ​​the cross-section At) (i.e., the total area of ​​the cross-section At). The same measurement is performed on 20 phase images, and the area ratios of the 20 are arithmetically averaged to obtain the "total particle area ratio (%)". Furthermore, the equivalent circle diameter is determined for each conductive particle present within the binarized rectangular region, and the particles are classified into large-diameter particles, medium-diameter particles, and small-diameter particles based on the equivalent circle diameter. Then, the total cross-sectional area Ab of the large-diameter particles, the total cross-sectional area Am of the medium-diameter particles, the total cross-sectional area As of the small-diameter particles, the number of cross-sectional areas Nb of the large-diameter particles, the number of cross-sectional areas Nm of the medium-diameter particles, the number of cross-sectional areas Ns of the small-diameter particles, and the average equivalent circle diameter are determined.

[0040] In this embodiment, the total particle area ratio is 9.0% or more and 14.5% or less, preferably 9.5% or more and 14.0%, and more preferably 10.0% or more and 13.0% or less. In the first embodiment, the proportion of large diameter areas in the endless belt is preferably 28.0% to 65.0%, more preferably 35.2% to 61.3%, and more preferably 42.2% to 60.0%. Furthermore, the proportion of large diameter elements in the endless belt of the first embodiment is preferably 3.5% to 13.7%, more preferably 3.8% to 13.7%, and even more preferably 3.8% to 13.0%. In the second embodiment, the proportion of large diameter areas in the endless belt is preferably 28.0% to 65.0%, more preferably 35.2% to 61.3%, and even more preferably 42.2% to 60.0%. Furthermore, the proportion of large diameter elements in the endless belt of the second embodiment is preferably 3.5% to 13.7%, more preferably 3.8% to 13.7%, and more preferably 3.8% to 13.0%.

[0041] In this embodiment, the mid-diameter area ratio is preferably 16.1% or more and 21.8% or less, more preferably 16.5% or more and 21.0% or less, and even more preferably 17.0% or more and 20.7% or less. Because the proportion of medium-diameter particles is within the above range, the density unevenness of the image is suppressed compared to the case where the total particle area ratio is within the above range, the proportion of large-diameter particles is within the above range, and the proportion of medium-diameter particles is smaller than the above range. The reason for this is not clear, but it is thought that because the number of small-diameter particles contained in the substrate layer is not too large, the distance between medium-diameter and large-diameter particles is kept at an appropriate level, making it easier to obtain electric field dependence. Furthermore, because the proportion of medium-diameter particles is within the above range, density unevenness in the image is suppressed compared to the case where the total particle area ratio is within the above range, the proportion of large-diameter particles is within the above range, and the proportion of medium-diameter particles is greater than the above range. The reason for this is not entirely clear, but it is thought that because the number of small-diameter particles contained in the substrate layer is not too small, current can flow between medium-diameter and large-diameter particles, which conduct current more easily than small-diameter particles, making it easier to obtain electric field dependence.

[0042] In this embodiment, the percentage of medium-diameter particles is preferably 7.5% or more and 13.5% or less, more preferably 8.0% or more and 13.5% or less, and even more preferably 8.0% or more and 13.0% or less. When the proportion of medium-sized particles is within the above range, the density unevenness in the image is suppressed compared to the case where the total particle area ratio is within the above range, the proportion of large-sized particles is within the above range, and the proportion of medium-sized particles is smaller than the above range. The reason for this is not clear, but it is presumed to be the same reason why the density unevenness in the image is suppressed when the proportion of medium-sized particles is within the above range, compared to the case where the total particle area ratio is within the above range, the proportion of large-sized particles is within the above range, and the proportion of medium-sized particles is smaller than the above range. Furthermore, when the proportion of medium-sized particles is within the above range, the density unevenness in the image is suppressed compared to when the total particle area ratio is within the above range, the proportion of large-sized particles is within the above range, and the proportion of medium-sized particles is greater than the above range. The reason for this is not clear, but it is presumed to be the same reason why the density unevenness in the image is suppressed when the proportion of medium-sized particles is within the above range, compared to when the total particle area ratio is within the above range, the proportion of large-sized particles is within the above range, and the proportion of medium-sized particles is greater than the above range.

[0043] In this embodiment, the average equivalent diameter of the circular area in the cross-section of the conductive particles is preferably 26.7 nm or more and 43.8 nm or less, more preferably 28.0 nm or more and 42.5 nm or less, and even more preferably 29.0 nm or more and 42.0 nm or less. It is presumed that by having the average equivalent circle diameter within the above range, the particle size does not become too small compared to when it is smaller than the above range, thereby achieving both suppression of density unevenness in the image and suppression of crack occurrence in the substrate layer. Furthermore, it is presumed that by having the average equivalent circle diameter within the above range, the particle size does not become too large compared to when it is larger than the above range, thereby achieving both suppression of density unevenness in the image and suppression of crack occurrence in the substrate layer.

[0044] The methods for controlling the total particle area ratio, large diameter area ratio, medium diameter area ratio, large diameter number ratio, medium diameter number ratio, and average circle equivalent diameter are not particularly limited. Examples include adjusting the particle size distribution and amount of conductive particles added in the process of forming the base material layer of an endless belt, adjusting the kneading time of a composition containing polymer material and conductive particles, and combining these methods.

[0045] <Layer configuration> The endless belt according to this embodiment has a base layer containing a polymer material and conductive particles. The endless belt according to this embodiment may have a release layer on at least one of the outer and inner surfaces of the base layer. When the endless belt is a laminate, the release layer may be provided only on the outer circumferential surface of the base layer, only on the inner circumferential surface of the base layer, or on both the outer and inner circumferential surfaces of the base layer. In addition, if necessary, other layers such as an elastic layer may be provided between the base layer and the release layer. Furthermore, the endless belt according to this embodiment may be a single-layer body consisting only of a base material layer, without a release layer.

[0046] Figure 1 is a schematic perspective view showing an example of an endless belt according to this embodiment. The endless belt 50 shown in Figure 1 has a base layer 52, a release layer 54, and a release layer 56. The release layer 54 is provided on the outer circumferential surface of the base layer 52 and is a layer that constitutes the outer circumferential surface of the endless belt 50. The release layer 56 is provided on the inner circumferential surface of the base layer 52 and is a layer that constitutes the inner circumferential surface of the endless belt 50.

[0047] In this embodiment, the endless belt preferably further has a release layer provided on at least one of the outer and inner surfaces of the base material layer. When a release layer is provided on the outer surface of the substrate layer, the recording medium or toner image becomes easier to separate from the surface of the endless belt when an endless belt is used as a transfer member (e.g., a secondary transfer belt or an intermediate transfer belt) in a transfer means for transferring a toner image to a recording medium. As a result, the load on the rotation of the endless belt during the transfer process is reduced. Furthermore, when a release layer is provided on the inner surface of the base material layer, and an endless belt is used as a transfer member in a transfer means for transferring a toner image to a recording medium, the sliding properties between the support member that supports the endless belt and the surface of the endless belt are improved, and the load on the rotation of the endless belt is reduced.

[0048] The layer structure and materials of the endless belt according to this embodiment will be described in detail below.

[0049] <Base material layer> The base layer is preferably a film or sheet containing conductive particles in a polymer material.

[0050] (polymer material) Examples of polymer materials include rubber and resin. A single polymer material may be used, or two or more may be used in combination.

[0051] Examples of rubbers include chloroprene rubber, epichlorohydrin rubber, isoprene rubber, butyl rubber, polyurethane, silicone rubber, fluororubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber (NBR), ethylene propylene rubber, ethylene-propylene-diene terpolymer rubber (EPDM), natural rubber, and mixtures thereof.

[0052] Examples of resins include polyamide, polyimide, polyamideimide, polyetherimide, polyetheretherketone, polyphenylene sulfide, polyethersulfone, polyphenylsulfone, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polycarbonate, polyester, and mixtures thereof.

[0053] Among these, the polymer material included in the base layer preferably contains ion-conductive rubber. Including ion-conductive rubber in the polymer material has the advantage of further reducing the effect of humidity on conductivity. Ionic conductive rubber is rubber that possesses ionic conductivity. For example, rubber exhibits conductivity through the dissociation and movement of ions. Examples of ionic conductive rubber include polar rubber, and more specifically, epichlorohydrin rubber (ECO) and chloroprene rubber (CR).

[0054] The polymer material contained in the base layer preferably includes at least one selected from the group consisting of epichlorohydrin rubber and chloroprene rubber, and more preferably chloroprene rubber. Including at least one selected from the group consisting of epichlorohydrin rubber and chloroprene rubber in the polymer material provides the advantage of being able to maintain a lower volume resistivity of the base layer compared to when the ion-conductive rubber contained in the polymer material is only a compound other than epichlorohydrin rubber and chloroprene rubber (e.g., EPDM).

[0055] The polymer material contained in the base layer may include compounds other than ion-conductive rubber. Examples of compounds other than ion-conductive rubber include ethylene propylene diene terpolymer rubber, acrylonitrile butadiene rubber, and urethane rubber. Among these, rubbers other than ion-conductive rubber are preferred, and among these rubbers, ethylene propylene diene rubber and acrylonitrile butadiene rubber are preferred from the viewpoint of humidity stability.

[0056] The polymer material contained in the base layer preferably contains both ion-conductive rubber and compounds other than ion-conductive rubber, more preferably contains at least one selected from the group consisting of epichlorohydrin rubber and chloroprene rubber and at least one selected from the group consisting of ethylene propylene diene terpolymer rubber and acrylonitrile butadiene rubber, and even more preferably contains both chloroprene rubber and ethylene propylene diene terpolymer rubber.

[0057] (Conductive particles) Examples of conductive particles include carbon black such as Ketjenblack, oil furnace black, channel black, and acetylene black; metal particles such as aluminum and nickel; and metal oxide particles such as indium tin oxide, tin oxide, zinc oxide, titanium oxide, and yttrium oxide. Carbon black is preferred as the conductive particle. One type of conductive particle may be used alone, or two or more types may be used in combination.

[0058] Among the conductive particles contained in the substrate layer, it is preferable that electronically conductive particles be included. Including electronically conductive particles makes it easier to obtain electric field dependence. Electronically conductive particles are particles that possess electronic conductivity, such as particles that exhibit conductivity through the movement of electrons. Examples of electronically conductive particles include carbon black, metal particles, and metal oxide particles, with carbon black being preferred among them. Furthermore, from the viewpoint of imparting conductivity, among carbon blacks, Ketjenblack and acetylene black, which have high conductivity, are preferred as conductive particles, and acetylene black, which has good compatibility with the resin, is more preferred.

[0059] The average primary particle size of the conductive particles is preferably 26.7 nm to 43.8 nm, more preferably 29.8 nm to 39.6 nm, and even more preferably 30.5 nm to 38.0 nm. Furthermore, when using two or more conductive particles with different average primary particle sizes, it is preferable that the average value of the primary particle size of all the conductive particles is within the above range.

[0060] The substrate layer may contain conductive agents other than conductive particles. Examples of conductive agents other than conductive particles include ionic conductive substances such as potassium titanate, potassium chloride, sodium perchlorate, and lithium perchlorate; and ionic conductive polymer materials such as polyaniline, polyether, polypyrrole, polysulfone, and polyacetylene. One conductive agent may be used alone, or two or more may be used in combination.

[0061] The base layer is preferably a conductive elastic layer containing rubber and conductive particles, and more preferably a conductive elastic layer containing at least one of chloroprene rubber and epichlorohydrin rubber and carbon black.

[0062] The total content of conductive particles and conductive agents in the base layer is preferably set based on the volume resistivity of the endless belt. The volume resistivity of the endless belt is 1.0 × 10⁻⁶. 7 Ω cm or more 1.0×10 11 It is preferable that the value be Ω·cm or less, and 1.0 × 10 7 Ω cm or more 5.0×10 10 It is preferable that the value be Ω·cm or less, and 1.0 × 10 7 Ω cm or more 3.0×10 10 It is preferable that the value is Ω·cm or less. In this embodiment, the volume resistivity (Ω·cm) is measured as follows. The measurement environment is 22°C and 55% relative humidity. The sample is placed in the measurement environment for more than 24 hours to control temperature and humidity. The resistance measuring instrument is a microammeter (Advantest R8430A), and the probe is a UR probe (Mitsubishi Chemical Corporation). The applied voltage is 1kV, the application time is 5 seconds, and the load is 1kgf. There are 18 measurement points in total: 6 points at equal intervals in the circumferential direction of the endless belt, and 3 points in the width direction of the endless belt, at the center and both ends. The arithmetic mean of the 18 measurements is calculated.

[0063] If the base layer contains carbon black, the carbon black content is preferably 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of polymer material.

[0064] The base layer may contain additives such as antioxidants, crosslinking agents, flame retardants, colorants, surfactants, dispersants, and fillers.

[0065] From the viewpoint of durability of the endless belt, the average thickness of the base layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. From the viewpoint of flexibility and bending resistance of the endless belt, it is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less.

[0066] <Release layer> The endless belt according to this embodiment may have a release layer on at least one of the outer and inner surfaces of the base material layer, and it is preferable that the base material layer has release layers on both the outer and inner surfaces. The release layer provided on the outer surface of the base material layer constitutes the outer surface of the endless belt. The release layer provided on the inner surface of the base material layer constitutes the inner surface of the endless belt.

[0067] The release layer is preferably a film or sheet containing a polymer material. Examples of polymer materials include the rubber and resins mentioned above, which were described for the base layer.

[0068] The release layer preferably contains urethane resin and fluorine-containing resin particles. Urethane resin (also called polyurethane or urethane rubber) is generally synthesized by polymerizing polyisocyanate and polyol. It is preferable that the urethane resin has both a hard segment and a soft segment.

[0069] As fluorine-containing resin particles, one or more of the following are preferred: tetrafluoroethylene resin, trifluoroethylene chloride resin, hexafluoropropylene resin, vinyl fluoride resin, vinylidene fluoride resin, difluoroethylene chloride resin, and copolymers thereof. Among these, tetrafluoroethylene resin particles are preferred as fluorine-containing resin particles.

[0070] The average primary particle size of the fluorine-containing resin particles is preferably 50 nm to 500 nm, more preferably 70 nm to 480 nm, and even more preferably 100 nm to 450 nm.

[0071] The release layer may contain additives such as antioxidants, crosslinking agents, flame retardants, colorants, and fillers.

[0072] The average thickness of the release layer on one side of the base layer is preferably 3.0 μm or more, more preferably 3.5 μm or more, and even more preferably 4.0 μm or more, from the viewpoint of wear resistance of the release layer, and preferably 12.0 μm or less, more preferably 10.5 μm or less, and even more preferably 9.0 μm or less, from the viewpoint of flexibility and bending resistance of the endless belt.

[0073] [Manufacturing method for endless belts] One example of a manufacturing method for an endless belt is to prepare a tubular member that will serve as the base layer and to form a release layer on the outer or inner surface of the tubular member.

[0074] Methods for manufacturing tubular members include, for example, extrusion molding, in which a composition containing a polymer material and conductive particles is melted and extruded in a belt shape from a die and solidified; injection molding, in which a composition containing a polymer material and conductive particles is melted and placed in a belt-shaped mold and solidified; and coating molding, in which a composition containing a polymer material precursor or monomer and conductive particles is applied to a core body and solidified.

[0075] Methods for forming a release layer include, for example, applying a liquid composition containing a polymer material and fluorine-containing resin particles to the outer or inner surface of a tubular member and allowing it to solidify; or applying a liquid composition containing a precursor or monomer of a polymer material and fluorine-containing resin particles to the outer or inner surface of a tubular member and allowing it to solidify. Depending on the type of components, drying, heating, electron beam irradiation, or ultraviolet irradiation may be performed to solidify the liquid composition.

[0076] <Belt Unit> Figure 2 is a schematic perspective view showing an example of a belt unit according to this embodiment. The belt unit 60 is a schematic perspective view showing an endless belt stretched across multiple roll members. The belt unit 60 comprises an endless belt 50, a drive roll 62, and a support roll 64, and has a configuration in which the endless belt 50 is stretched across the drive roll 62 and the support roll 64 under tension (hereinafter also referred to as "tensioned"). The drive roll 62 rotates due to the power of a drive unit (not shown) connected to the drive roll 62. The endless belt 50 and the support roll 64 rotate in accordance with the rotation of the drive roll 62.

[0077] The belt unit 60 is incorporated into an electrophotographic image forming apparatus as part of the transfer means. The belt unit 60 is suitable for a secondary transfer belt unit. The number of roll members that tension the endless belt 50 in the belt unit 60 is not limited to two, but may be three or more.

[0078] <Image forming apparatus> The image forming apparatus according to this embodiment comprises a photoreceptor, a charging means for charging the surface of the photoreceptor, an electrostatic image forming means for forming an electrostatic image on the charged surface of the photoreceptor, a developing means for containing a developer containing toner and using the developer to develop the electrostatic image formed on the surface of the photoreceptor to form a toner image, and a transfer means having a belt unit according to this embodiment for transferring the toner image to a recording medium. The transfer means, for example, comprises an intermediate transfer body, a primary transfer means for transferring the toner image to the surface of the intermediate transfer body, and a secondary transfer means for transferring the toner image transferred to the surface of the intermediate transfer body to a recording medium, wherein the secondary transfer means has the belt unit according to this embodiment.

[0079] The image forming apparatus according to this embodiment may further include fixing means for fixing a toner image transferred to the surface of a recording medium; photoreceptor cleaning means for cleaning the surface of the photoreceptor before it is charged after the transfer of the toner image; and static elimination means for irradiating the surface of the photoreceptor with static elimination light to remove static charge after the transfer of the toner image before it is charged. The part of the image forming apparatus according to this embodiment that includes the developing means may be a cartridge structure (process cartridge) that can be attached to and detached from the image forming apparatus.

[0080] The following describes an example of an image forming apparatus according to this embodiment, but it is not limited to this example. In the following description, only the main parts shown in the figures will be described, and other parts will be omitted.

[0081] Figure 3 is a schematic diagram showing an example of an image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 3 is equipped with first to fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side at predetermined distances from each other in the horizontal direction. These units 10Y, 10M, 10C, and 10K may also be process cartridges that can be attached to and detached from the image forming apparatus.

[0082] An intermediate transfer belt (an example of an intermediate transfer body) 20 extends above each unit 10Y, 10M, 10C, and 10K, passing through each unit. The intermediate transfer belt 20 is wound around a drive roll 22 and a support roll 24, which are in contact with the inner surface of the intermediate transfer belt 20, and is configured to travel in the direction from the first unit 10Y to the fourth unit 10K. The support roll 24 is subjected to a force moving away from the drive roll 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around both. An intermediate transfer belt cleaning device 30 is provided on the image holding surface side of the intermediate transfer belt 20, facing the drive roll 22.

[0083] Each of the developing devices (examples of developing means) for each unit 10Y, 10M, 10C, and 10K, 4Y, 4M, 4C, and 4K, is supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0084] Since the first to fourth units 10Y, 10M, 10C, and 10K have equivalent configurations and operations, the first unit 10Y, which forms the yellow image and is located upstream of the intermediate transfer belt's travel direction, will be described as a representative example.

[0085] The first unit 10Y has a photoreceptor 1Y. Around the photoreceptor 1Y are, in order, a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential, an exposure device (an example of a charge image forming means) 3 that exposes the charged surface with a laser beam 3Y based on a color-separated image signal to form a charge image, a developing device (an example of a developing means) 4Y that supplies charged toner to the charge image to develop the charge image, a primary transfer roll (an example of a primary transfer means) 5Y that transfers the developed toner image onto an intermediate transfer belt 20, and a photoreceptor cleaning device 6Y that removes toner remaining on the surface of the photoreceptor 1Y after primary transfer.

[0086] The primary transfer roll 5Y is positioned inside the intermediate transfer belt 20, facing the photoreceptor 1Y. Each primary transfer roll 5Y, 5M, 5C, and 5K of each unit is connected to a bias power supply (not shown) that applies the primary transfer bias.

[0087] The belt unit 60 is a belt unit equipped with an endless belt 50 (an example of an endless belt according to this embodiment). The belt unit 60 comprises the endless belt 50, a drive roll 62, and a support roll 64. The belt unit 60 is positioned outside the intermediate transfer belt 20 and opposite the support roll 24. A bias power supply (not shown) for applying a secondary transfer bias is connected to the belt unit 60.

[0088] The following describes the process of forming the yellow image in the first unit 10Y. First, prior to operation, the surface of the photoreceptor 1Y is charged to a potential of -600V to -800V by the charging roll 2Y. The photoreceptor 1Y is conductive (for example, has a volume resistivity of 1 × 10 at 20°C). -6 The photosensitive layer is formed by laminating a photosensitive layer on a substrate (less than Ωcm). This photosensitive layer normally has high resistance (resistance of general resin), but when irradiated with a laser beam, the resistivity of the irradiated area changes. Therefore, a laser beam 3Y is irradiated from the exposure device 3 onto the surface of the charged photoreceptor 1Y according to image data for yellow sent from a control unit (not shown). As a result, an electrostatic charge image of the yellow image pattern is formed on the surface of the photoreceptor 1Y.

[0089] A static charge image is an image formed on the surface of a photoreceptor 1Y due to charging. It is a so-called negative latent image formed when the resistivity of the irradiated portion of the photoreceptor layer decreases due to the laser beam 3Y, causing the charged material on the surface of the photoreceptor 1Y to flow, while the charge remains in the portion not irradiated by the laser beam 3Y. The electrostatic charge image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves. At this development position, the electrostatic charge image on the photoreceptor 1Y is developed as a toner image by the developing device 4Y and made visible.

[0090] The developing device 4Y contains, for example, an electrostatic image developer including at least yellow toner and a carrier. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y and is held on the developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the static charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image on the surface of the photoreceptor 1Y, and the latent image is developed by the yellow toner. The photoreceptor 1Y, on which the yellow toner image has been formed, continues to move at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0091] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y acts on the toner image, transferring the toner image on the photoreceptor 1Y onto the intermediate transfer belt 20. The transfer bias applied at this time has a polarity opposite to the toner's polarity (-) (+), and in the first unit 10Y, it is controlled by a control unit (not shown) to, for example, +10 μA.

[0092] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K from the second unit 10M onward is also controlled in accordance with the first unit. Thus, the intermediate transfer belt 20, on which the yellow toner image has been transferred in the first unit 10Y, is sequentially transported through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and transferred in multiple layers.

[0093] The intermediate transfer belt 20, on which four toner images have been multiple-transferred through the first to fourth units, proceeds to a secondary transfer section consisting of the intermediate transfer belt 20, a support roll 24, and a belt unit 60. Meanwhile, recording paper (an example of a recording medium) P is fed via a supply mechanism into the gap where the belt unit 60 and the intermediate transfer belt 20 are in contact, at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has the same polarity (-) as the toner's polarity (-), and an electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection means (not shown) that detects the resistance of the secondary transfer section, and is voltage-controlled.

[0094] The recording paper P onto which the toner image has been transferred is fed to the contact area (nip area) of a pair of fixing rolls in a fixing device (an example of a fixing means) 28, where the toner image is fixed onto the recording paper P, and a fixed image is formed. The recording paper P, on which the color image has been fixed, is discharged towards the discharge area, and the series of color image formation operations is completed.

[0095] Examples of recording paper P used to transfer the toner image include plain paper used in electrophotographic photocopiers and printers. Other recording media besides recording paper P include OHP sheets. [Examples]

[0096] The embodiment will be described in more detail below with reference to examples, but this embodiment is not limited to the following examples. Unless otherwise specified, synthesis, processing, and manufacturing were carried out at room temperature (25°C ± 3°C).

[0097] <Manufacturing of an endless belt> (Preparation of the base layer) A rubber composition was prepared by blending each of the following components in the amounts (parts by mass) listed in Table 1. EPDM: (Ethylene propylene diene rubber, JSR Corporation EP33) CR: (Chloroprene rubber, manufactured by Tosoh Corporation, TSR-61) CB1: (Acetylene black, manufactured by Denka Co., Ltd., product name: Denka Black Granules, average primary particle size: 35 nm) CB2: (Acetylene black, manufactured by Denka Co., Ltd., product name: Denka Black HS-100, average primary particle size: 48 nm) CB3: (Acetylene black, manufactured by Denka Co., Ltd., product name: Denka Black FX-35, average primary particle size: 23 nm) Sulfur: (Manufactured by Tsurumi Chemical Industry Co., Ltd.) ZnO: (manufactured by Kyodo Kagaku) Vulcanization accelerator: (Noxellar M, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Stearic acid

[0098] A rubber composition containing the above components in the proportions shown in Table 1 was fed into a kneading extruder, kneaded for the time shown in Table 1, then extruded and hot-air dried to obtain a tubular body with a diameter (outer diameter) of 40 mm and an average thickness of 490 μm. The tubular body was cut to a length of 355 mm to be used as a base material.

[0099] [Table 1]

[0100] (Preparation of protective layer) A PTFE (polytetrafluoroethylene)-containing urethane resin (Bonderite T862A, Henkel Japan) was mixed with a hardening agent (Loctite WH-1, Henkel Japan) at a concentration of 1% by mass, and then diluted with water to prepare a coating solution. The coating solution was sprayed onto the outer surface of the substrate while rotating it with its central axis oriented horizontally. Then, hot air drying was performed at 150°C for 35 minutes to form a protective layer with an average thickness of 6 μm on the outer surface of the substrate. Next, the same coating solution was sprayed onto the inner surface of the substrate, and hot air drying was performed in the same manner to form a protective layer with an average thickness of 6 μm on the inner surface of the substrate. In this way, an endless belt having protective layers on both sides of the base layer was obtained.

[0101] <Cross-sectional observation of the substrate layer and measurement of the endless belt> Following the previously described method, section samples of the endless belt were prepared, and the total particle area ratio (%), large diameter area ratio (%), medium diameter area ratio (%), large diameter number ratio (%), medium diameter number ratio (%), and average equivalent circle diameter (nm) of conductive particles contained in the substrate layer were determined. The results are shown in Table 2. Furthermore, the volume resistivity of the endless belt was measured according to the method described above. The results are shown in Table 2.

[0102] [Table 2]

[0103] <Performance evaluation of endless belts> (Dependence of resistance on electric field) The endless belt was placed in an environment with a temperature of 22°C and a relative humidity of 55% for more than 24 hours to control temperature and humidity. Under the same temperature and humidity conditions, the resistance value (unit: log(Ω)) was measured using a microammeter (Advantest, R8430A) and a UR probe (Mitsubishi Chemical Corporation) under the measurement conditions of applied voltage: 100V or 500V, application time: 5 seconds, and load: 1kgf. Measurement points were set at 3 points in the width direction of the endless belt (center and both ends) and 6 points at equal intervals in the circumferential direction, for a total of 18 points. The arithmetic mean of the 18 measured values ​​for each applied voltage of 100V and 500V was calculated, and the difference between the average value for 100V and the average value for 500V was classified as follows. The results are shown in Table 3. A: Difference of 1 or more B: Difference is 0.8 or more but less than 1 C: Difference is less than 0.8

[0104] (Image quality - uneven density and color fading) The transfer performance of the endless belt was evaluated based on image density unevenness and color fading. The endless belt of the example or comparative example was mounted as a secondary transfer belt in the Versant 3100i Press image forming apparatus (Fujifilm Business Innovation Co., Ltd.). The image forming apparatus was placed in an environment of 22°C and 55% relative humidity for more than 24 hours, and under the same conditions, a black halftone image with an image density of 30% was formed on the entire surface of one side of an A3 size sheet of paper.

[0105] Density unevenness was evaluated by measuring the image density of the halftone images using an X-Rite404 density meter (X-Rite Corporation). Measurement points were set at 3 points in the center and both ends of the long side of an A3 size paper, and 3 points in the center and both ends of the short side of an A3 size paper, for a total of 9 points. The difference between the maximum and minimum image density values ​​at these 9 points was classified as follows. The results are shown in Table 3. G1: Difference is less than 0.05 G2: Difference between 0.05 and less than 0.15 G3: Difference of 0.15 or more

[0106] Regarding color loss, the presence or absence of color loss in halftone images was visually observed and evaluated according to the following criteria. The results are shown in Table 3. G1: No color loss was observed at all. G2: Slight discoloration was observed, but it was within acceptable limits. G3: Color fading was observed and exceeded the acceptable range.

[0107] (Flexural resistance) In accordance with JIS-P8115:2001, an endless belt was repeatedly bent using an MIT testing machine with a sample width of 15 mm and a tensile load of 1 kg. The surface of the endless belt was visually inspected every 500,000 bends (one cycle being one reciprocal), and the timing of crack initiation was classified as follows. The results are shown in Table 3. A: No cracks appeared after 2 million bending cycles. B: Cracks appear after 2 million bending cycles. C: Cracks appeared after 1.5 million bending cycles. D: Cracks appear after fewer than 1 million bending cycles.

[0108] [Table 3]

[0109] From the above results, it can be seen that this embodiment achieves both suppression of image density unevenness and suppression of crack formation in the substrate layer of the endless belt, compared to the comparative example. [Explanation of symbols]

[0110] 50 Endless belt 52 Base material layer 54 Release layer 56 Release layer 60 Belt Units 62 Drive Roll 64 Support Rolls

[0111] 1Y, 1M, 1C, 1K photoconductor 2Y, 2M, 2C, 2K Charging Rolls (Example of Charging Method) 3. Exposure apparatus (an example of electrostatic image formation means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing apparatus (an example of a developing method) 5Y, 5M, 5C, 5K Primary Transfer Rolls (Example of Primary Transfer Method) 6Y, 6M, 6C, 6K Photoconductor Cleaning Device 8Y, 8M, 8C, 8K Toner Cartridges 10Y, 10M, 10C, 10K Image Forming Units 20. Intermediate transfer belt (an example of an intermediate transfer body) 22 Drive Roll 24 Support Rolls 28 Fixing device (an example of a fixing means) 30 Intermediate Transfer Belt Cleaning Device 50 Endless belt 60 Belt Units 62 Drive Roll 64 Support Rolls P Recording paper (an example of a recording medium)

Claims

1. It has a substrate layer containing a polymer material and carbon black, In an image obtained by observing a cross-section cut along the thickness direction of the substrate layer using an atomic force microscope, the ratio of the total area Ap of the cross-section of the entire carbon black is 9.0% or more and 14.5% or less of the total area At of the cross-section of the substrate layer, and the area of ​​the carbon black cross-section is 0.01 μm. ２ The ratio of the total cross-sectional area Ab of the carbon black to the total cross-sectional area Ap of the carbon black is 28.0% or more and 65.0% or less. Used as a transfer material, Endless belt.

2. The endless belt according to claim 1, wherein the ratio of the total cross-sectional area Ap of the entire carbon black is 9.5% or more and 14.0% or less of the total cross-sectional area At of the base material layer.

3. The area is 0.01 μm ２ The endless belt according to claim 1 or claim 2, wherein the ratio of the total cross-sectional area Ab of the carbon black is 35.2% or more and 61.3% or less of the total cross-sectional area Ap of the entire carbon black.

4. The area of ​​the cross-section of the carbon black is 0.005 μm ２ The above 0.01 μm ２ The endless belt according to any one of claims 1 to 3, wherein the proportion of the total cross-sectional area Am of carbon black that is less than 16.1% or more and 21.8% or less of the total cross-sectional area Ap of the entire carbon black.

5. It has a substrate layer containing a polymer material and carbon black, In an image obtained by observing a cross-section cut along the thickness direction of the substrate layer using an atomic force microscope, the ratio of the total area Ap of the cross-section of the entire carbon black is 9.0% or more and 14.5% or less of the total area At of the cross-section of the substrate layer, and the area of ​​the carbon black cross-section is 0.01 μm. ２ The ratio of the number of particles Nb in the cross-section of the carbon black is as described above. The proportion of the total number of cross-sections Np is between 3.5% and 13.7%. Used as a transfer material, Endless belt.

6. The area of ​​the cross-section of the carbon black is 0.005 μm ２ The above 0.01 μm ２ The endless belt according to claim 5, wherein the proportion of carbon black cross-sections with a number of particles Nm less than 7.5% to 13.5% of the total number of carbon black cross-sections Np.

7. The polymer material comprises ion-conductive rubber, as described in any one of claims 1 to 6, for the endless belt.

8. The endless belt according to claim 7, wherein the ion-conductive rubber includes at least one selected from the group consisting of epichlorohydrin rubber and chloroprene rubber.

9. The endless belt according to any one of claims 1 to 8, wherein the average circular equivalent diameter in the cross-section of the carbon black is 26.7 nm or more and 43.8 nm or less.

10. The endless belt according to any one of claims 1 to 9, further comprising a release layer provided on at least one of the outer and inner surfaces of the base material layer.

11. An endless belt according to any one of claims 1 to 10, The system comprises a plurality of roll members over which the endless belt is stretched under tension, It is attached to and detached from the image forming apparatus. Belt unit.

12. Photoreceptor and A charging means for charging the surface of the photoreceptor, A means for forming an electrostatic image on the surface of the charged photoreceptor, A developing means containing a developer containing toner, and using the developer to develop the electrostatic charge image formed on the surface of the photoreceptor to form a toner image, A belt unit according to claim 11, and a transfer means for transferring the toner image to a recording medium, An image forming apparatus equipped with the following features.

13. The transfer means, The system comprises an intermediate transfer body, a primary transfer means for transferring the toner image to the surface of the intermediate transfer body, and a secondary transfer means for transferring the toner image transferred to the surface of the intermediate transfer body to a recording medium. The secondary transfer means comprises the belt unit described in claim 11, The image forming apparatus according to claim 12.

Images